1. Field of the Invention
The present invention relates to a hydro-mechanical transmission of a vehicle, and, more particularly, to the controlling of the shifting process of a hydro-mechanical transmission in a vehicle such as a combine.
2. Description of the Related Art
Agricultural vehicles utilize transmissions to change gear ratios to drive the vehicle over the ground at various speeds. The transmission of a heavy piece of equipment such as an agricultural harvester, also known as a “combine”, has to be effectively shifted in order to achieve a required ground speed and torque to perform required harvesting operations without any operator discomfort. A combine is historically termed such because it combines multiple harvesting functions with a single harvesting unit, such as picking, threshing, separating and cleaning A combine includes a header which removes the crop from a field, and a feeder housing which transports the crop matter into a threshing rotor. The threshing rotor rotates within a perforated housing, which may be in the form of adjustable concaves and performs a threshing operation on the crop to remove the grain. Once the grain is threshed it falls through perforations in the concaves onto a grain pan. From the grain pan the grain is cleaned using a cleaning system, and is then transported to a grain tank onboard the combine. A cleaning fan blows air through the sieves to discharge chaff and other debris toward the rear of the combine. Non-grain crop material, such as straw, from the threshing section proceeds through a residue system, which may utilize a straw chopper to process the non-grain material and direct it out the rear of the combine. When the grain tank becomes full, the combine is positioned adjacent a vehicle into which the grain is to be unloaded, such as a semi-trailer, gravity box, straight truck, or the like; and an unloading system on the combine is actuated to transfer the grain into the vehicle.
More particularly, the engine, by way of the transmission provides power to the drive wheels or tracks of the vehicle. In order to achieve required speed and torque during machine operation, up and down shifting of the transmission is carried out by swapping clutch engagements. In order to achieve a large speed range, the difference of output to input gear ratios for first and second gear is generally significantly large (usually the output to input gear ratio for second gear is more than twice the gear ratio of the first gear). Due to this large difference in the gear ratios, the task of shifting gears without interruption in vehicle speed felt by the operator driving the vehicle becomes very critical. Such shifting can lead to a jerk of the vehicle, which can impact the comfort of the operator and other systems of the vehicle.
What is needed in the art is a shifting algorithm that shifts the transmission in a smooth and efficient manner.